This invention relates to apparatus for removing solids for coke oven tar in a flushing liquor separation decanter, and particularly to a drag assembly having endless travel means with screen member elements thereon.
"Flushing liquor decanters" are well known devices used for separating tar from flushing liquor in coke plants. Such devices are shown for example in U.S. Pat. Nos. 3,923,659 and 4,282,096. The separation process is described in U.S. Pat. No. 4,176,062. The decanters are rather large vessels, for example, of generally rectangular shape. A typical decanter might be 50 feet long, 14 feet wide and 10 feet high. Such a decanter would be designed to receive 2,000 to 5,000 gallons per minute of flushing liquor and to recover 2 to 15 gallons per minute of tar from the liquor. Flushing liquor and tar are desirably passed from the decanter at the same rates, respectively as that which they enter. Exit flow of tar from the decanter is controlled by a simple weir. The conventional decanter includes a continuous drag system for removing solids which settle with the tar to the bottom of the decanter.
With the advent of the use of pulverized coal in coke oven practice, significant quantities of coal and coke particles enter with the flushing liquor. The large coal and coke particles settle to the bottom of the decanter and are removed by the conventional drag system. The smaller particles combine and agglomerate with tar and moisture to form "goobers" which float within the tar. These agglomerates eventually build up and plug the weir reducing and sometimes stopping the outlet flow of tar. The resultant increase or building of the tar level must be reduced. The necessary reduction of tar level detracts from tar quality, especially causing variation and elevation in the moisture level and quinoline insoluable ("QI") content of the tar.
A chain conveyor having screen elements thereon for removing solid animal matter from sewage contained in a semi-cylindrical tank in a tannery is shown in U.S. Pat. No. 1,769,655. The chain conveyor rides on a drum having a cylindrical surface formed of a screen so that all the liquid passes into the drum and is filtered by the screen prior to removal of the liquid from the tank. The screen elements project downwardly from the conveyor to sweep solids from the space between the drum and the bottom curved surface of the semi-cylindrical tank. The reference system does not suggest a coke oven decanter drag assembly having screen elements, nor such an assembly having solid spindles as distinguished from the screen surface of the drum as shown in the reference.
U.S. Pat. No. 3,891,558 shows a conveyor with arc-shaped buckets of screen material for allowing liquid to drain from solid material as it is conveyed in the buckets on the conveyor. This reference does not suggest the use of conveyor apparatus having screen elements in a highly viscous material such as tar contained in a flushing liquor decanter. Nor does the reference suggest a drag assembly in a coke oven decanter having planar screen elements as distinguished from the arc-shaped screens shown.